Hydraulic hammers are used on work sites to break up large hard objects before such objects can be moved away. Hydraulic hammers may be mounted to back hoes or excavators, or may be hand-held. Typically, the hammer assembly is powered by either a hydraulic or pneumatic pressure source. During a work or power stroke, high fluid pressure is applied to a first shoulder of a piston, thereby driving the piston in a forward direction. The piston then strikes a work tool, which is driven in the forward direction thereby causing a work tip of the tool to strike the rock, concrete, asphalt or other hard object to be broken up. During a return stroke, fluid pressure is applied to a second shoulder of the piston in order to return the piston to its original position.
The work tool, also known as a tool bit, is retained within a sleeve, commonly referred to as a front head. When the tool is driven forward, the kinetic energy of the tool is transferred to the object to be broken up. However, if full contact with the object to be broken up does not occur, a proportion of the energy is transferred to the front head. If no contact takes place with the object to be broken up, then all of the energy may be transferred to the front head. Consequently, the front head is subject to cyclical loading which tends to pull it away from the cylinder of the hammer assembly. Conventionally, external tie rods are used to tie the front head to the cylinder. The tie rods increase the overall diameter of the hammer assembly and add to the complexity of manufacture. Tie rods typically have to be replaced at regular service intervals, since they are subject to fatigue failure and failure of a tie rod can cause irreparable damage to the entire hammer assembly.